The invention relates to a process for the preparation of acyloxybenzenesulfonates starting from carbonyl halides and salts of phenolsulfonic acid which have a low water content.
Acyloxybenzenesulfonic acids and their salts are compounds which have been known for a long time. Depending on the chain length of the acyl group, they can be used as surfactants, bleach activators or in other applications. These compounds may be obtained by reacting sodium phenolsulfonate (SPS) with the chloride of an organic carboxylic acid. The reaction medium used is organic solvents such as methylene chloride (U.S. Pat. No. 3,503,888), high-boiling hydrocarbons (U.S. Pat. No. 4,704,236; EP 220 826), xylene or toluene (EP 164 786). According to U.S. Pat. No. 5,069,828, this reaction is carried out in an aprotic organic solvent in the presence of a phase transfer catalyst.
U.S. Pat. No. 6,448,431 (WO 01/19 771) describes the reaction of acyl chlorides with SPS in trifluoroacetic acid (TFA) as solvent. In the examples, the ratio of TFA:SPS used is from 0.5:1 to 3:1. The high cost of TFA, its complete removal from the reaction mixture, and possible transesterification reactions or the formation of byproducts, however, prevents the utilization of the process on an industrial scale.
All of the processes have the problem that virtually anhydrous SPS must be used for the reaction since otherwise acyl halide or the finished ester are hydrolyzed in the presence of water, which leads to considerable losses in yield. SPS is available commercially as dihydrate with a water content of about 15%. Conventional drying can reduce the water content to about 2%. According to U.S. Pat. No. 5,069,828, it is possible to remove the remaining amount of water by azeotropic distillation in the presence of an entrainer such as xylene. However, due to the high time requirement, this is of little use in plants which operate continuously. Alternatively, the water content can be reduced to less than 1% by drying in an inert or vacuum atmosphere by techniques well known to those skilled in the art. However, as is known from U.S. Pat. No. 4,666,636, which is hereby incorporated by reference, that certain drying conditions must be observed exactly in order to maintain the reactivity of the SPS. If those drying conditions are not followed, SPS can participate in a number of secondary reactions, as a result of which both the degree of conversion of the subsequent acylation, and also the color of the end products is significantly impaired. Over drying of the SPS leads to degrees of conversion of less than 50% in the subsequent acylation reaction.
To solve this problem it is recommended in DE 101 39 663.5 (U.S. application Ser. No. 10/209,723, filed Aug. 1, 2002) to add nitrogen containing compounds such as DMF or NMP. This increases the degree of conversion, but problems arise regarding the filtration of the reaction mixture. In addition problems arise with malodor.
It is therefore an object of the present invention to develop a process which can be carried out industrially and also continuously, which leads, in very good yields, to the most uniform products possible which, with regard to composition, grade and color, are suitable for use in laundry detergents and cleaners. In this connection, the process should be independent of the grade of the sodium phenolsulfonate used and its pretreatment.
Surprisingly, it has now been found that acyloxybenzenesulfonates can be prepared in high yields and good grades, irrespective of the relative reactivity or grade of the SPS used, if the reaction of the SPS with an alkanecarboxylic acid derivative is carried out in an aliphatic or aromatic solvent in the presence of 0.5 to 25% by weight of a polyglycol ether.
In one embodiment, invention relates to a process for the preparation of acyloxybenzenesulfonates by reaction of phenolsulfonates which have a water content of less than 0.5% by weight, preferably less than 0.2% by weight, of water with alkanecarboxylic acid derivatives in an aliphatic or aromatic hydrocarbon, which comprises carrying out the reaction in the presence of from 0.5 to 25% by weight of a polyglycol ether of the formula
Rxe2x80x94Oxe2x80x94CR1R2CR1R2xe2x80x94(Oxe2x80x94CR1R2CR1R2)xxe2x80x94Oxe2x80x94R3
wherein R and R3 are C1 to C4 alkyl, R1 and R2 are hydrogen or C1 to C2 alkyl and x is a number from 1 to 4.
In another embodiment, the invention relates to a process for the continuous production of acyloxybenzenesulfonate. The continuous process comprises passing a phenolsulfonate compound, which has a water content of less than 0.5, and an alkanecarboxylic acid derivative to a continuous reaction zone. The continuous reaction zone contains a mother liquor comprising an aliphatic or aromatic hydrocarbon, in the presence of from 0.5 to 25 weight % of a polyglycol ether to provide a reaction mixture. At effective conditions, the reaction mixture is reacted to provide a crude acyloxybenzenesulfonate. The crude acyloxybenzenesulfonate from the mother liquor; and at least a first portion of the mother liquor is returned to the continuous reaction zone. In the continuous reaction zone during the reaction step, at least a portion of the water reacts with the alkanecarboxylic acid derivative to form impurities. In order to minimize the buildup of the impurities in the mother liquor, a second portion of the mother liquor is regenerated to remove at least a portion of the impurities. A regenerated mother liquor is returned to the continuous reaction zone.